The present application claims the benefit of earlier filed U.S. Provisional Application No. 60/010,763, entitled PRODUCTION OF NANOSTRUCTURED MATERIALS BY HYPERSONIC PLASMA PARTICLE DEPOSITION filed on Jan. 29, 1996.
The present invention relates to nanostructured materials. Further, the present invention relates to a method and apparatus for production of such materials.
The synthesis and processing of nanophase or nanostructured materials, i.e. materials with grain sizes less than about 100 nm, is of great interest as such materials are known to have properties different from and often superior to those of conventional bulk materials. Examples include greater strength, hardness, ductility, and sinterability; size dependent light absorption, greater reactivity etc. There has been considerable progress in determining the properties of nanophase materials, small amounts of which have been synthesized (mainly as nanosize powders) by a number of processes including colloidal precipitation, mechanical grinding, and gas-phase nucleation and growth. Extensive reviews have documented recent developments in nanophase materials (Gleiter, H. (1989) "Nanocrystalline materials," Prog. Mater. Sci. 33:223-315); (Siegel, R. W. (1993) "Synthesis and properties of nanophase materials," Mater. Sci. Eng. A168:189-197). The potential applications of nanophase materials include wear resistant coatings, thermal barrier coatings, ductile ceramics, new electronic and optical devices, catalysts etc. However, before the benefits of this emerging technology can be realized in the form of commercial products, two challenging problems need to be addressed, namely, (1) controlled, high-rate synthesis of nanosize powders, and (2) assembly of these powders into nanostructured materials. Controlled synthesis implies that the particles are uniform in size, composition and morphology, and are substantially unagglomerated, and generally requires that the consolidation or assembly be done in-situ to avoid contamination.
Gas-phase nucleation and growth of particles is an established route for the synthesis of nanosize powders (Gleiter, H. (1989) "Nanocrystalline materials," Prog. Mater. Sci. 33:223-315) and includes such techniques as evaporation-condensation (Recknagle, K., Leung, A., Brown, D., Martian, P., Chung, J. N., Xia, Q., Hamilton, H. and Crowe, C. T. (1995) "Design and operation of a nanocluster generation and collection system," Aerosol Sci. Technol. 22:3-10 1995) and (Oda, M., Katsu, I., Tsuneizumi, M., Fuchita, E., Kashu, S. and Hayashi, C. (1993) "Ultrafine particle films by gas deposition method,"Mat. Res. Soc. Symp. Proc. 286:121-130), laser pyrolysis (Flint, J. H., Marra, R. A. and Haggerty, J. S. (1986) "Powder temperature, size and number density in laser-driven reactions," Aerosol Sci. Technol. 5:249-260) and thermal plasma expansion (Rao, N., Girshick, S., Heberlein, J., McMurry, P., Jones, S., Hansen, D., Micheel, B. (1995) "Nanoparticle formation using a plasma expansion process," Plasma Chem. Plasma Proc., 15(4):581-606 and Rao, N., Micheel, B., Hansen, D., Fandrey, C., Bench, M., Girshick, S., Heberlein, J., and McMurry, P. H. (1995) "Synthesis of nanophase silicon, carbon and silicon carbide powders using a plasma expansion process," J. Mater. Res. 10(8):2073-2084). In many of these gas-phase processes, the nanosize powders were collected thermophoretically and consolidated in-situ using high pressure compaction (Gleiter, H. (1989) "Nanocrystalline materials," Prog. Mater. Sci. 33:223-315) and (Recknagle, K., Leung, A., Brown, D., Martian, P., Chung, J. N., Xia, Q., Hamilton, H. and Crowe, C. T. (1995) "Design and operation of a nanocluster generation and collection system," Aerosol Sci. Technol. 22:3-10) to produce pellets of nanostructured materials.
The use of impinging jets for materials processing is based on the fact that heavy particles seeded in a light carrier gas can be deposited efficiently by expanding the particle-gas mixture through a nozzle and directing the resulting jet against an impaction substrate (Marple, V. A. (1970) "A Fundamental Study of Inertial Impactors," Ph.D. Thesis, Mechanical Engineering Department, University of Minnesota, Minn.), (Fernandez de la Mora, J. (1985) "Surface impact of seeded jets at relatively large background densities," J. Chem. Phys. 82:3453-3464) and (Fernandez de la Mora, J., Hering, S. V., Rao, N. and McMurry, P. H. (1990) "Hypersonic impaction of ultrafine particles," J. Aerosol Sci. 21:169-187). The host gas is decelerated as it approaches the impaction substrate, whereas the heavy particles, provided they are larger than a certain critical size, continue their forward motion and impact by virtue of their greater inertia. The critical particle size for impaction to occur depends on the nozzle geometry, gas properties (pressure, temperature, composition and velocity), and particle properties (density, shape etc.) . In the past, impaction of heavy particles had been a useful technique for particle size measurement (Fernandez de la Mora, J., Hering, S. V., Rao, N. and McMurry, P. H. (1990) "Hypersonic impaction of ultrafine particles," J. Aerosol Sci. 21:169-187) and for collecting particle samples for microscopic analysis (Rao, N., Micheel, B., Hansen, D., Fandrey, C., Bench, M., Girshick, S., Heberlein, J., and McMurry, P. H. (1995) "Synthesis of nanophase silicon, carbon and silicon carbide powders using a plasma expansion process," J. Mater. Res. 10(8):2073-2084). In recent times, however, a number of materials deposition processes based on impaction principles have been developed, including those that deposit heavy molecules (Schmitt, J. J. (1988) "Method and apparatus for the deposition of solid films of a material from a jet stream entraining the gaseous phase of said material," U.S. Pat. No. 4,788,082) and (Halpern, B. L., Schmitt, J. J., Golz, J. W., Johnson, D. L. (1991) "Gas jet deposition of thin films," Appl. Surf. Sci. 48/49:19-26), ultrafine particles (Kashu, S., Fuchita, E., Manabe, T. and Hayashi, C. (1984) "Deposition of ultrafine particles using a gas jet," Japn. J. Appl. Phys. 23:L910-912), (Oda, M., Katsu, I., Tsuneizumi, M., Fuchita, E., Kashu, S. and Hayashi, C. (1993) "Ultrafine particle films by gas deposition method," Mat. Res. Soc. Symp. Proc. 286:121-130) and (Hayashi, C. (1987) "Ultrafine Particle Spraying Apparatus," U.S. Pat. No. 4,657,187) and large micron-sized particles (Calcote, H. F. and Felder, W. (1992) "A new gas-phase combustion synthesis process for pure metals, alloys, and ceramics," pp.1869-1876 in 24th Symp. (Intl.) on Combustion, Combustion Inst., Pittsburgh) and (Gould, R. K. and Dickson, C. R. (1991) "Apparatus for producing high purity silicon from flames of sodium and silicon tetrachloride," U.S. Pat. No. 5,021,221). These processes also differ widely in the source of deposited materials, the flow and pressure regimes used for impaction, as well as the microstructure of the materials produced. Related processes wherein nozzle generated cluster beams at far lower pressure also have been used for producing thin films (Haberland, H., Karrais, M., Mall, M. and Thurner, Y. (1992) "Thin films from energetic cluster impact: a feasibility study,." J. Vac. Sci. Technol. A 10(5):3266-3271) and (U.S. Pat. No. 5,110,435) and nanocrystalline deposits (Perez, A., Melinon, P., Paillard, V., Dupuis, V., Jensen, P., Hoareau, A., Perez, J. P., Tuaillon, Broyer, M., Vialle, J. L., Pellarin, M., Baguenard, B., and Lerme, J. (1995) "Nanocrystalline Structures Prepared by Neutral Cluster Beam Deposition," Nanostructured Materials 6:43-52). In general, the smaller the particles to be deposited, the higher the flow speeds, and the lower the pressures required for impaction to occur. For particles in the nanometer size regime, a highly supersonic (i.e. hypersonic) flow may be used for impaction (Fernandez de la Mora, J., Hering, S. V., Rao, N. and McMurry, P. H. (1990) "Hypersonic impaction of ultrafine particles," J. Aerosol Sci. 21:169-187). In such hypersonic impactors, the seeded gas flow expands through a nozzle into a vacuum, and the flow downstream of the nozzle is accelerated to very high Mach numbers, on the order of 5. The gas is then rapidly decelerated in the shock layer formed ahead of the impaction substrate, while heavy particles larger than the critical size are impacted, forming a deposit.
The high particle kinetic energies associated with hypersonic impaction may be used to activate physical and/or chemical transformations at the deposition surface. An example of such a transformation was demonstrated for the case of heavy molecules by Fernandez de la Mora, J. (1985) "Surface impact of seeded jets at relatively large background densities," J. Chem. Phys. 82:3453-3464, who decomposed W(CO).sub.6 molecules seeded in hydrogen gas by hypersonic impaction against a clean surface. A solid non-volatile coating was formed on the impaction surface. More recently, Hamza, A. V., Balooch, M. and Moalem, M. (1994) "Growth of silicon carbide films via C.sub.60 precursors," Surf. Sci. 317:L1129-L1135 have produced silicon carbide structures by impacting a molecular beam of fullerenes against a heated silicon substrate. A similarly high velocity reactive deposition process for nanosized particles is suggested by recent molecular dynamics simulations of argon nanoparticles impacting at 3 km/s (Cleveland, C. L. and Landman, U. (1992) "Dynamics of Cluster-Surface Collisions," Science 257:355-361). These simulations have determined that the atoms in the impacting particle are inertially confined in a transient (picosecond) chemically reacting environment characterized by extreme local density (up to 50% above normal liquid density), pressure (&gt;10 GPa), and kinetic temperature (.about.4000K). They suggest that the intense, transient, "nano-shock" phenomena associated with the compressed non-equilibrium environment may initiate new modes of chemical reactions, which are then quenched by rapid energy exchange with the temperature-controlled substrate (Cheng, H.-P. and Landman, U. (1993) "Controlled deposition, soft landing, and glass formation in nanocluster-surface collisions," Science 260:1304-1307).